This invention relates generally to flexible optical waveguides and, more particularly, to flexible waveguides for the transmission of laser beams at relatively high power levels, such as from pulsed lasers.
In recent years, lasers have been shown to be useful in a variety of medical, dental and industrial applications. Many such applications require the transmission of laser energy at relatively high powers from a laser to an area of application. In some cases, the laser itself can be portable or movable, but this is often impracticable, and there is then the requirement for a reliable and efficient waveguide to transmit the laser energy from a stationary laser source to the area of application. Clearly, such a waveguide must be relatively light in weight, not easily damaged by routine use, and, most importantly, it must be flexible enough to allow convenient and accurate application of the laser energy to any desired area. It will be apparent that a waveguide satisfying these requirements may also be usefully applied for the transmission of incoherent light at relatively high power levels, usually for the purposes of illumination.
One type of waveguide which in part meets these requirements consists of a series of mirrors arranged along an articulated arm, the laser beam being reflected from mirror to mirror along the arm. However, it will be apparent that such an arrangement has only limited flexibility, and is sensitive to errors in alignment, as well as being bulky and relatively expensive to manufacture and maintain.
Another general type of light waveguide employs the principle of total internal reflection to transmit light along a column or core of material, usually quartz or glass. If the material of the core has a refractive index higher than that of a cladding material, light incident on the junction between core and cladding will be almost totally reflected if the angle of incidence, measured from a line normal to the junction, is greater than a critical value. Thus, light can be transmitted along the fiber and reflected around bends, provided that their radius is not too small. The principal problem with optical fibers of this kind is that they must be very thin to provide the required flexibility. Thin fibers of quartz or the like are necessarily quite fragile, and present great difficulties for the transmission of large amounts of power. In laser applications, the power densities in thin fibers can be high enough to breakdown the material, and using bundles of fibers bonded together does not completely solve the problem, since breakdown can still occur in the cladding and bonding materials which absorb radiation directly. Thin fibers also present problems of alignment with a laser source and accurate "launching" of the light beam into the fibers.
Some optical fibers of this type have been formed from finely drawn quartz capillary tubes filled with a liquid, but the same problems of fragility, alignment, and breakdown of the material, prevent their use in any of the aforementioned applications requiring high power levels.
A flexible light guide comprising a liquid-filled plastic tube has been proposed in a patent to Cass, U.S. Pat. No. 3,740,113. However, the materials disclosed and suggested therein render such a light guide completely unsuitable for the transmission of laser energy, or even of high-power incoherent light.
Accordingly, there is a need, recognized by those familiar with the laser art and its potential applications, for a flexible waveguide which is capable of transmitting laser energy at high power, and which meets the other requirements described above. The aforementioned patent application, of which this application is a continuation-in-part, discloses and claims a liquid-core waveguide which has largely fulfilled the need for most areas of application. However, the core liquids disclosed and claimed therein have certain limitations which render them unsuitable in some applications. More specifically, under certain conditions, these core liquids: lack color stability when exposed to heat and high-intensity light; have varying degrees of toxicity rendering them unsuitable for some medical applications; and are volatile, a property which increases the difficulty of manufacture. Furthermore, changes in temperature cause differential thermal expansion between the liquid and cladding materials, usually resulting in the formation of bubbles and voids in waveguides which are permanently sealed at the ends. The present invention provides significant improvements in these areas over the waveguide disclosed and claimed in the parent application.